Spinal implant surface configuration with a projection having a back cut

ABSTRACT

The present invention is a specialized implant having opposed surfaces for engaging each of the vertebral bodies adjacent a disc space into which the implant is implanted. The surface comprises arrayed projections having at least one forward facing facet directed at least in part toward the leading end of the implant and at least one rearward portion directed at least in part toward the opposite trailing end of the implant. Each of the forward facet and rearward portion has a length and a slope. The length of the forward facet is longer than the length of the rearward facet. The slope of the rearward facet is steeper than the slope of the forward facet. The surface projections also have opposed side facets directed generally toward the sides of the implant. The side facets are located between the forward facet and rearward facet and converge toward each other in a direction away from the base of the surface projections. The surface may also include projections having left and right forward side facets and a rearward facet. The surface further may include projections having left and right rearward side facets and a forward facet.

This application is a continuation of application Ser. No. 09/457,228,filed Dec. 8, 1999, now U.S. Pat No. 6,827,740, which is incorporatedherein by reference.

BACKGROUND OF THE INVENTION Description Of The Related Art

The present invention relates to interbody spinal implants for placementbetween adjacent vertebral bodies of a human spine, and morespecifically to a specialized surface for such interbody implants, forengaging the adjacent vertebral bodies. Vital to the functioning of allinterbody spinal implants is their ability to remain properly locatedwithin the spine after installation. In U.S. Pat. Nos. 5,593,409 and5,609,635, Michelson described the use of surface roughenings, such asknurling or ratcheting on the opposed upper and lower vertebral bodyengaging surfaces of interbody spinal fusion implants. Knurling has beenparticularly beneficial for increasing the grip of the implant surfaceto the adjacent vertebral bodies in a rather uniform manner without adirectional bias. Spinal implants have a propensity to move in aparticular direction, which is opposite to their path of insertion,because this is the path of least resistance. Such propensity to move isfurther increased when the opposed upper and lower vertebral bodyengaging surfaces are in angular relationship to each other, such thatthey are spaced further apart at the implant's trailing end than at theimplant's leading end. In such circumstances where it is desirable thento gain stability in resistance to a particular direction of movement ofthe interbody spinal implant, the use of a plurality of forward facingratchetings on the implant's vertebral body engaging surfaces has beenpreferable to the previously described knurling for that purpose.

The term “ratcheting” as used herein is defined as a plurality ofangular teeth or ridges or protrusions projecting from the surface of animplant to resist motion of the implant at least in one direction. Thephrase “forward facing ratchetings” as used herein is defined as aratcheting having at least one forward facing facet having a lengthgreater than a rearward facing facet and an angle from the implantsurface from which the forward facing facet arises that is less steepthan the angle of the rearward facet. On an implant surface, forwardfacing ratchetings facilitate the insertion of the implant in onedirection and after insertion, resisting movement of the implant in adirection opposite to the direction of insertion. An example of forwardfacing ratchetings of the prior art is shown in partial fragmentary viewin FIGS. 24A and 24B, generally referred to by the reference numeral 50.

Knurled surfaces of the related art provide some stability in alldirections, but lack the ability to resist a particular direction ofmotion preferentially. The above-described ratcheted surface bestresists motion in a particular direction. There exists a need for animproved interbody spinal implant surface configuration, wherein theopposed upper and lower vertebral body engaging surfaces of the implantare configured to be resistant to implant movement in all directions,and preferentially or in particularly in one direction.

SUMMARY OF THE INVENTION

The present invention relates to interbody spinal implants having aspecialized surface configuration on the opposed exterior surfacesadapted for engaging the vertebral bodies adjacent a disc space intowhich the interbody implant is to be implanted. Such an implant surfaceconfiguration has utility with a wide variety of shapes of interbodyspinal implants where enhanced skeletal fixation is desired. Such animplant surface configuration can provide for enhanced stability,increased surface area, and a surface for the delivery of fusionpromoting substances other than bone. In a preferred embodiment, theimplant surface can provide for resisting motion in all directions, andparticularly in at least one direction, such as counter to the directionof insertion of the implant.

While various embodiments of the present invention are presented by wayof example only and not limitation, common to each of them is that thesurface configuration incorporates a plurality of spatially integratedsurface projections having at least one forward facing facet directed atleast in part toward the leading end of the implant and at least onerearward portion directed at least in part toward the opposite trailingend of the implant. By way of example and not limitation, the rearwardportion may be a facet, a line, or an edge of the rearward aspect of thesurface projection formed where two facets come together. Each of theforward and rearward facets have a length and a slope. The length of theforward facet is longer than the length of the rearward facet. The slopeof the rearward facet is steeper than the slope of the forward facet. Invarious embodiments, the surface projections also have opposed sidefacets directed generally toward the sides of the implant. The sidefacets are located between the forward facet and rearward facet and mayconverge toward each other in a direction away from the base of thesurface projections. The surface comprises multifaceted ratchetedprojections that are organized in geometrically disposed fields orarrays which are at a minimum located on at least a portion of theopposed vertebral body engaging surfaces of the implant. From theteachings disclosed herein, it is appreciated that the surfaceprojections can be geometrically arranged in a pattern wherein at leasta portion of the projection is aligned along a longitudinal, horizontal,diagonal, or curved line. The upper and lower surfaces of the implantcan be at least in part arcuate or planar and can converge along aportion or all of the length of the implant.

In various preferred embodiments of the present invention, the rearwardfacets of the surface projections can be perpendicular or at anglesgreater or less than 90 degrees to at least one of the upper or lowersurfaces of the implant from which the projections arise. The opposedside facets of the surface projections can have at least a first portionin a plane at an angle to the longitudinal axis of the implant. Theopposed side facets can intersect each other, and can converge to form apeak at the top of each of the surface projections. The peaks can bealigned along lines that are perpendicular, parallel, or diagonal to thelongitudinal axis of the implant. The surface projections can be cleavedsuch as by longitudinal and/or horizontal cuts to increase the number ofexposed sides of the projections and thus increase the available surfacearea to contact and engage the bone of the adjacent vertebral bodies andincrease the number of recessed areas to contain fusion promotingsubstances. Alternatively, the peaks of each surface projection can becleaved, truncated, or flattened at least in part.

The surface projections can include a left forward side facet and aright forward side facet directed toward the leading end and sides,respectively, of the implant. Similarly, the surface projections caninclude a left rearward side facet and a right rearward side facetdirected toward the trailing end and sides, respectively, of theimplant. The side facets of adjacent surface projections can be spacedapart to define a groove therebetween. A plurality of adjacent surfaceprojections can be spaced apart to form a plurality of grooves that canbe parallel or at an angle to the longitudinal axis of the implant,wherein the angle can be less than 90 degrees. The grooves can have ahorizontal cross section that is a V-shape, U-shape, or a box-likeshape, for example.

Sequential projections can be positioned on an implant wherein eachsurface projection has forward facing facets facing the same direction,such that consecutive projections are oriented forward facing facet torearward facing facet. The lower most portion of the slope of theforward facing facet of a first surface projection in a sequence can becoincident with the rearward facet of the next surface projection in thesequence. Alternatively, the forward facet of a first surface projectionand the rearward facet of the next surface projection in a sequence canbe spaced apart and the space can be at least in part flat, curved, orany other surface contour suitable for the intended use. The surfaceprojections can be oriented relative to one another to form fields orarrays that further can be geometrically disposed relative to oneanother, preferably in a pattern wherein at least a portion of theprojection is aligned along a longitudinal, horizontal, diagonal, orcurved line.

The surface configuration of the present invention can be formed bycasting, machining, or any other techniques known to one of ordinaryskill in the art. The present surface configuration may readily bemachined by milling the implant surface from side to side, across theupper and lower vertebral body engaging surfaces, to form ratchetingsgenerally disposed perpendicular to the long axis of the implant andgenerally formed facing to the insertion end of the implant. Theratchetings may be cross machined with an angled cutting face to formgrooves passing through the ratchetings. For example, a milling machinehaving a cutting tool, with a V-shaped profile, can be run through theplurality of ratchetings parallel to the longitudinal axis of theimplant to form the above-described surface. In a preferred embodiment,the V-shaped cutting tool of the milling machine has opposed cuttingfaces with an angle of approximately 90 degrees to each other, whichfaces are each at a 45-degree angle to the plane of the surfaces beingmachined. Without departing from the scope of the present invention, theangle of the cutting faces can be more or less than 90 degrees, and theangle of the cutting face to the surface to be cut can be more or lessthan 45 degrees. It is appreciated that rather than the cutting elementbeing run parallel to the longitudinal axis of the implant, the cuttingelement could be run at some other angle. By way of example only and notlimitation, this angle could be at 45 degrees to the longitudinal axisof the implant and to the projections. Each surface projection couldthen be formed by a cutter crossing in two passes to form two grooves ata 90 degree angle to each other.

The surface of the present invention for engaging each of the adjacentvertebral bodies may be incorporated into various types of spinalimplants. Such spinal implants may be for the purpose of achievinginterbody spinal fusion, or for stabilizing a device to space apart andallow motion between the adjacent vertebral bodies. Such spinal implantsmay comprise any artificial or naturally occurring material appropriatefor the intended purpose. Such materials would include, but are notlimited to, implant quality metals, including, but not limited to,titanium and its alloys, surgical grade plastics and plastic compositeswhich may or may not be bioresorbable, ceramics, and cortical bone. Someexamples of interbody spinal implants that may benefit from the presentteaching, include but are not limited to the following patents andapplications by Michelson which are incorporated by reference herein:U.S. Pat. Nos. 5,015,247; 5,522,899; 5,593,409; 5,609,635; 5,860,973;and application Ser. No. 08/480,904.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of an interbody spinal implant having asurface configuration in accordance with the present invention.

FIG. 1A is a perspective view of an implant having arcuate surfaces andan end cap in accordance with an embodiment of the present invention.

FIG. 1B is a top elevational view of an implant having a leading end, atrailing end, and sides forming a circle in accordance with anembodiment of the present invention.

FIG. 1C is a graphical representation of a motion preserving device inaccordance with an embodiment of the present invention.

FIG. 2 is a side elevation view of the spinal implant of FIG. 1.

FIG. 3 is a side elevation view of the interbody spinal implant of FIG.1 installed in an implantation site formed across the disc space betweentwo adjacent vertebral bodies of the spine shown in partialcross-section.

FIG. 4 is an enlarged fragmentary top plan view of an implant surface ofone embodiment of the present invention from a view taken along area 4of FIG. 1.

FIG. 5 is a fragmentary side elevation view of the implant surface ofFIG. 4 from a view taken along area 5 of FIG. 2.

FIG. 6 is a fragmentary end elevation view of FIG. 4.

FIG. 7 is a fragmentary perspective view of the implant surface of FIG.4.

FIG. 8 is an enlarged fragmentary top plan view of a second embodimentof the implant surface of the present invention from a view taken alongarea 8 of FIG. 1.

FIG. 9 is a fragmentary side elevation view of the implant surface ofFIG. 8 from a view taken along area 9 of FIG. 2.

FIG. 10 is a fragmentary end view of the implant surface of FIG. 8.

FIG. 11 is a fragmentary perspective view of the implant surface of FIG.8.

FIG. 12A is an enlarged fragmentary top plan view of a third embodimentof the implant surface of the present invention from a view taken alongarea 12 of FIG. 1.

FIG. 12B is an enlarged fragmentary top plan view of another embodimentof the implant surface of the present invention from a view taken alongarea 12 of FIG. 1.

FIG. 13 is a fragmentary side elevation view of the implant surface ofFIG. 12A from a view taken along area 13 of FIG. 2.

FIG. 14 is a fragmentary end view of FIG. 12A.

FIG. 14A is an enlarged fragmentary side view of a groove having aU-shape in accordance with an embodiment of the present invention from aview taken along area 14A of FIG. 14.

FIG. 14B is an enlarged fragmentary side view of a groove having abox-shape in accordance with an embodiment of the present invention froma view taken along area 14B of FIG. 14.

FIG. 14C is a fragmentary end view of a plurality of surface projectionsspaced apart from one another in accordance with an embodiment of thepresent invention.

FIG. 15 is a fragmentary perspective view of the implant surface of FIG.12A.

FIG. 16 is an enlarged fragmentary top plan view of a fourth embodimentof the implant surface of the present invention from a view taken alongarea 16 of FIG. 1.

FIG. 17 is a fragmentary side elevation view of the implant surface ofFIG. 16 from a view taken along area 17 of FIG. 2.

FIG. 18 is a fragmentary end view of FIG. 16.

FIG. 19A is an enlarged fragmentary perspective view of the implantsurface of FIG. 16.

FIG. 19B is an enlarged fragmentary perspective view of a variation onthe second and third surface projections of the fourth embodiment of theimplant surface of the present invention with a cleave therethrough.

FIG. 20 is an enlarged fragmentary top plan view of a fifth embodimentof the implant surface of the present invention from a view taken alongarea 20 of FIG. 1.

FIG. 21 is a fragmentary side elevation view of the implant surface ofFIG. 20 from a view taken along line 21 of FIG. 2.

FIG. 22 is a fragmentary end view of FIG. 20.

FIG. 23 is an enlarged fragmentary perspective view of the implantsurface of FIG. 20.

FIGS. 24A and 24B are perspective and side elevation views,respectively, of a prior art implant surface having forward facingratchetings.

DETAILED DESCRIPTION OF THE DRAWINGS

As shown in FIGS. 1-7, an interbody spinal implant 100 has a leading end102, a trailing end 104, an upper surface 106, a lower surface 108, anda side wall 110 between upper and lower surfaces 106, 108. Upper andlower surfaces 106, 108 may converge from trailing end 104 to leadingend 102 along a longitudinal axis L of implant 100 as shown, or maydiverge, be parallel, or any combination thereof. Upper and lowersurfaces 106, 108 are configured to be placed against and in contact orengagement with the bone of vertebral bodies V of two adjacent vertebraeadjacent disc D of the human spine. Upper and lower surfaces 106,108 andside wall 110 may include large and/or small openings 112, 114, and 116,respectively, to permit bone growth into and through implant 100. Upperand lower surfaces 106,108 of implant 100 can be generally planar asshown in the figures, or can be opposed arcuate surfaces as shown anddescribed in U.S. Pat. No. 5,593,409, incorporated herein by reference,or any other configuration suitable for the desired use.

As shown in detail in FIGS. 4-7, at least a portion of upper and lowersurfaces 106, 108 of implant 100 have a surface configuration generallyreferred to by the numeral 120. In accordance with a first embodiment ofthe present invention, surface configuration 120 includes surfaceprojections 122 configured to facilitate insertion of implant 100 intoan implantation site while resisting expulsion of implant 100 in adirection opposite to the direction of insertion. Each of surfaceprojections 122 has an angled forward facet 124 directed at least inpart toward leading end 102 of implant 100 and a rearward facet 126directed at least in part toward trailing end 104 of implant 100.Forward facet 124 has a length greater than the length of rearward facet126. Rearward facet 126 has a slope that is steeper than the slope offorward facet 124. In this embodiment, the base of rearward facet 126forms an angle of approximately 90 degrees with respect to upper and/orlower surfaces 106, 108 of implant 100. It is appreciated that the angleof the base of rearward facet 126 with respect to upper and/or lowersurfaces 106, 108 of implant 100 may be perpendicular to, greater thanperpendicular to, or less than perpendicular to the base of the surfacewhere the facet arises. Forward facet 124 forms an angle in the range ofapproximately 10 to 60 degrees, with 25-45 degrees being preferred, withrespect to upper and/or lower surfaces 106, 108. Each one of surfaceprojections 122 also has a left side facet 132 and a right side facet134 directed toward the sides of implant 100.

In this embodiment of surface configuration 120, a plurality of surfaceprojections 122 are spaced apart laterally (side to side) bylongitudinal grooves 130 formed along the longitudinal axis L of implant100. In one embodiment, longitudinal grooves 130 have a V-shapedhorizontal cross-section. The lower most portions of left and right sidefacets 132, 134 of consecutive side-by-side projections 122 can becoincident with each other or may be spaced apart, any spacetherebetween can be at least in part flat, curved, sloped or otherwiseconfigured. Each surface projection 122 has left and right side facets132, 134 that converge to form a high point or peak 136 at the top ofeach surface projection 122. Each peak 136 can be aligned along linesthat are perpendicular, parallel, and/or diagonally oriented tolongitudinal axis L of implant 100. The left and right side facets 132,134 resist side-to-side motion of implant 100 after it is inserted intothe implantation space. Peaks 136 engage the bone of vertebral bodies Vadjacent to implant 100 in the implantation site. It is appreciated thatin a variation of the present invention, the peaks may be modified suchas to be truncated or cut off to have a broader rather than sharperupper most surface. Moreover, the peaks can be cleaved in one or moredirections so as to increase the surface area useful for engaging thebone of the vertebral bodies. The relieved areas of the cleavedprojections are useful for containing and carrying fusion promotingsubstances other than bone such as bone morphogenetic proteins andgenetic materials coding for the production of bone, or bone itselfwhich could by way of example be in the form of a paste. It is furtherappreciated that for all the various embodiments of the surfaceconfiguration of the present invention, longitudinal grooves 130 canhave horizontal cross-sections in a variety of configurations such as,without limitation, square-shaped or U-shaped configurations.

Sequential projections can be positioned on an implant wherein eachsurface projection has forward facing facets facing the same directionsuch that consecutive projections are oriented forward facing facet torearward facing facet. The lower most portion of the slope of theforward facing facet of a first surface projection in a sequence can becoincident with the rearward facet of the next surface projection in thesequence. Alternatively, the forward facet of a first surface projectionand the rearward facet of the next surface projection in a sequence canbe spaced apart and the space can be at least in part flat, curved, orany other surface configuration suitable for the intended use. Thesurface projections can be oriented relative to one another to form anarray and are preferably geometrically disposed relative to one anotherin a pattern wherein at least a portion of the projection is alignedalong a longitudinal, horizontal, diagonal, or curved line. Further, itis appreciated that the surface of the present invention can be usefulwith spinal implants of various configurations, including configurationswherein at least one of leading end, trailing end, and sides of thespinal implant is curved. By way of example and not limitation, theleading end, trailing end, and sides of the spinal implant can form anoval, an oblong, or a circle. As shown in FIGS. 8-11, a secondembodiment of the surface configuration of the present invention isgenerally referred to by the numeral 220. Surface configuration 220includes surface projections 222 to facilitate insertion of implant 100into an implantation site while resisting expulsion of implant 100 in adirection opposite to the direction of insertion. Each of surfaceprojections 222 has an angled forward facet 224 directed at least inpart toward leading end 202 of implant 100 and a rearward facet 226directed at least in part toward trailing end 204 of implant 100.Forward facet 224 has a length greater than the length of rearward facet226. Rearward facet 226 has a slope that is steeper than the slope offorward facet 224. In this embodiment, the base of rearward facet 226forms an angle of approximately 45 degrees with respect to upper and/orlower surfaces 206, 208 of implant 100. Each one of surface projections222 has a left side facet 232 and a right side facet 234 directed towardthe sides of implant 100, and forward facet 224 and rearward facet 226.

In this embodiment of surface configuration 220, longitudinal grooves230 have a V-shaped horizontal cross-section. The lower most portions ofleft and right side facets 232, 234 of consecutive side-by-sideprojections 222 can be coincident with each other or may be spacedapart, any space therebetween can be at least in part flat, curved,sloped or otherwise configured. Each surface projection has left andright side facets 232, 234 that converge to form a high point or peak236 at the top of each surface projections 222. Each peak 236 can bealigned along lines that are perpendicular, parallel, and/or diagonallyoriented to the longitudinal axis L of implant 100. The left and rightside facets 232, 234 resist side-to-side motion of implant 100 after itis inserted into the implantation space. Peaks 236 engage the bone ofthe vertebral bodies adjacent to implant 100 in the implantation site.

As shown in FIGS. 12-15, a third embodiment of the surface configurationof the present Invention is generally referred to by the numeral 320 isshown. Surface configuration 320 includes surface projections 322 tofacilitate insertion of implant 100 into an implantation site whileresisting expulsion of implant 100 in a direction opposite to thedirection of insertion. Each of surface projections 322 has an angledforward facet 324 directed at least in part toward leading end 302 ofimplant 100 and a rearward facet 326 directed at least In part towardtrailing end 304 of implant 100. Forward facet 324 has a length greaterthan the length of rearward facet 326. Rearward facet 326 has a slopethat is steeper than the slope of forward facet 324. In this embodiment,the base of rearward facet 326 is “back cut” to form an angle greaterthan 90 degrees with respect to upper and/or lower surfaces 306, 308 ofimplant 100. The rearward facet 326 and the forward facet 324 have anegative direction of inclination, i.e., a negative slope, as shown inFIG. 13. The configuration of rearward facet 326 further enhancesresistance of motion of the implant in a direction opposite to thedirection of insertion. It is appreciated that the angle of the base ofrearward facet 326 with respect to upper and/or lower surfaces 306, 308of implant 100 can be any other angle suitable for the intended purposeof the present invention. Each one of surface projections 322 has a leftside facet 332 and a right side facet 334 directed toward the sides ofimplant 100, and a forward facet 324 and a rearward facet 326.

In this embodiment of surface configuration 320, longitudinal grooves330 have a V-shaped horizontal cross section. The lower most portions ofleft and right side facets 332, 334 of consecutive side-by-sideprojections 322 can be coincident with each other or may be spacedapart, and any space therebetween can be at least in part flat, curved,sloped or otherwise configured. Each surface projection 322 has left andright side facets 332, 334 that converge to form a high point or peak336 at the top of each surface projection 322. Each peak 336 can bealigned along lines that are perpendicular, parallel, and/or diagonallyoriented to the longitudinal axis L of implant 100. The left and rightside facets 332, 334 resist side-to-side motion of implant 100 after itis inserted into the implantation space. Peaks 336 engage the bone ofvertebral bodies V adjacent to implant 100 in the implantation site.

As shown in FIGS. 16-19B, a fourth embodiment of the surfaceconfiguration of the present invention is generally referred to by thenumeral 420. Surface configuration 420 includes surface projections 422configured to facilitate insertion of implant 100 in the direction ofinsertion into an implantation site while resisting expulsion of implant100 in a direction opposite to the direction of insertion. Each ofsurface projections 422 has an angled forward facet 424 directed towardleading end 402 of implant 100 and a rearward portion 426 directedtoward trailing end 404 of implant 100. Forward facet 424 has a lengthgreater than the length of rearward portion 426. Rearward portion 426has a slope that is steeper than the slope of forward facet 424. In thisembodiment, the base of rearward portion 426 forms an angle ofapproximately 90 degrees with respect to upper and/or lower surfaces406, 408 of implant 100. Rearward portion 426 can be a portion ofsurface projection 422, such as a facet, an edge, or a line for example.Each one of surface projections 422 has a left side forward facet 450, aright side forward facet 452, a left side rearward facet 454, and aright side rearward facet 456 directed toward the front and sides, anddirected toward the rear and sides of implant 100, respectively, andforward facet 424 and rearward portion 426.

Surface configuration 420 can further include a second plurality ofsurface projections 460 having at least a left forward side facet 462and a right forward side facet 464 directed at least in part towardleading end 402 and sides of implant 100, respectively, and at least onerearward facet 466 directed at least in part toward trailing end 400.Left and right forward side facets 462, 464 have at least a firstportion in a plane at an angle to the longitudinal axis of implant 100.Second surface projections 460 can be interspersed with surfaceprojections 422.

Surface configuration 420 can further comprise a third plurality ofsurface projections 470 having at least a left rearward side facet 472and a right rearward side facet 474 directed at least in part towardtrailing end 404 and sides of implant 100, respectively, and at leastone forward facet 476 directed at least in part toward leading end 402.Left and right rearward side facets 472, 474 have at least a firstportion in a plane at an angle to the longitudinal axis of implant 100.Third surface projections 470 can be interspersed with surfaceprojections 422 and/or second surface projections 460. Surfaceprojections 422 may have a length approximating the combined length ofsecond surface projections 460 and third surface projections 470.

In this embodiment, surface configuration 420 has angled grooves 440 a-kthat form a plurality of surface projections 422. In this example,angled grooves 440 a-k are formed at an angle that is approximately 45degrees to longitudinal axis L of spinal implant 100 and in thisexample, angled grooves 440 a-k are approximately 90 degrees to oneanother. The angled grooves 440 a-k can be formed, if machined, by firstpassing a cutting element at a 45 degree angle to the longitudinal axisL of implant 100 and then passing the cutting element at a 90 degreeangle to the path of the first pass of the cutting element, or otherwiseformed by casting, molding, and other methods for forming a surfaceconfiguration. It is appreciated that angled grooves 400 a-k can beformed at various angles to the longitudinal axis L of implant 100 andto each other. For example, such angles can be less than 180 degrees.

In this embodiment of surface configuration 420, angled grooves 440 a-khave a V-shaped horizontal cross-section. Each surface projection 422has left and right side facets 432 and 434 that are convergent and forma high point or peak 436 at the top of each surface projections 422.Each peak 436 can be aligned along lines that are horizontally,longitudinally, and/or diagonally oriented along implant 100. The leftand right side forward and rearward facets 450, 452, 454, 456 functionto prevent side-to-side motion of implant 100 after it is inserted intothe implantation space. Peaks 436 may also function like teeth to engagethe bone of vertebral bodies V adjacent to the implant in theimplantation site.

FIG. 19B shows a variation of second and third surface projections 460′,470′ that can be cleaved in one or more directions to increase thenumber of exposed sides of each projection and thus increase the surfacearea of the implant bone engaging surface available to contact the boneof the vertebral bodies. A preferred embodiment of this variation of thesecond and third surface projections 460′, 470′ are cleaved by alongitudinal groove.

As shown in FIGS. 20-23, a fifth embodiment of the surface configurationof the present invention is generally referred to by the numeral 520.Surface configuration 520 includes surface projections 522 to facilitateinsertion of implant 100 into an implantation site while resistingexpulsion of implant 100 in a direction opposite to the direction ofinsertion. Surface projections 522 can be cleaved in one or moredirections to increase the number of exposed sides of each projectionand thus increase the surface area of the implant bone engaging surfaceavailable to contact the bone of the vertebral bodies. For example, thesurface projections can be cleaved by a longitudinal cut 540 generallyparallel to the longitudinal axis L of implant 100 to form a surfaceprojection having nine exposed sides. The surface projections mayfurther be cleaved by a horizontal cut 542 generally perpendicular tothe longitudinal axis L of implant 100 to form a surface projectionhaving eighteen exposed sides. The cuts can penetrate the surfaceprojection at a depth substantially equal to that of the height of thesurface projections as measured from the upper or lower surfaces of theimplant. The cuts can be oriented along at least one of the longitudinalaxis of the implant, an axis perpendicular to the longitudinal axis ofsaid implant, and an axis at an angle between the longitudinal axis andthe axis perpendicular to the longitudinal axis of the implant. It isappreciated that cuts 540 and 542 may be formed as part of the moldingprocess for forming the surface projections.

When cleaved by longitudinal cut 540 and horizontal cut 542, each ofsurface projections 522 has angled forward facet 524 a, 524 b directedat least in part toward leading end 502 of implant 100 and rearwardfacets 526 a, 526 b directed at least in part toward trailing end 504 ofimplant 100. Forward facet 524 has a length greater than the length ofrearward facet 526. Rearward facets 526 a, 526 b have a slope that issteeper than the slope of forward facets 524 a, 524 b. The cleavedportion of surface projection 522 can be spaced apart by a predetermineddistance and the space can be at least in part flat, curved, or anyother surface configuration suitable for the intended use. In thisembodiment, the base of rearward facets 526 a, 526 b forms an angle ofapproximately 45 degrees with respect to upper and/or lower surfaces506, 508 of implant 100. Each one of surface projections 522 has leftside facets 532 a, 532 b and right side facets 534 a, 534 b directedtoward the sides of implant 100, and forward facets 524 a, 524 b andrearward facet 526 a, 526 b. In this embodiment of surface configuration520, longitudinal grooves 530 have a V-shaped horizontal cross-sectionand each surface projection 522 has left and right side facets 532 a,532 b, 534 a, 534 b that converge toward one another. The left and rightside facets 532 a, 532 b, 534 a, 534 b resist side-to-side motion ofimplant 100 after it is inserted into the implantation space. Thesurface configuration of the present invention can be formed by molding,machining or otherwise. A preferred surface configuration of the presentinvention may readily be machined by milling from side to side, acrossthe upper and lower vertebral body engaging surfaces, surfaceprojections. A milling machine with a cutting tool having an angledcutting face such as a V-shaped profile can then be run through theplurality of surface projections parallel to the longitudinal axis ofthe implant to form the above-described surface. In a preferredembodiment, the V-shaped cutting tool of the milling machine has faceswith an angle of approximately 90 degrees, which faces are at a45-degree angle to the plane of the surfaces being so machined. Withoutdeparting from the present invention, the angle of the cutting faces canbe more or less than 90 degrees, the angle of the cutting face to thesurface to be cut can be more or less than 45 degrees, and rather thanrunning the cutter element parallel to the longitudinal axis of theimplant, the cutting element may be run at an angle. By way of exampleonly and not limitation, this angle may be at 45 degrees to thelongitudinal axis of the implant and each surface projection can beformed by two grooves crossing the projections at a 90 degree angle toeach other.

The spinal implants of the present invention are made of artificial ornaturally occurring materials suitable for implantation in the humanspine. The implants can comprise bone including, but not limited to,cortical bone, materials other than bone, such as metals including, butnot limited to, titanium and its alloys or ASTM material, surgical gradeplastics, plastic composites, ceramics, or other materials suitable foruse as a spinal implant. The implants of the present invention canfurther comprise or be combined with bone growth promoting materials,including but not limited to, bone, bone morphogenetic proteins,hydroxyapatite, and genes coding for the production of bone. Theimplants can be treated with a bone growth promoting substance, can be asource of osteogenesis, or can be bioabsorbable at least in part. Theimplants of the present invention can be formed of a porous material.

The spinal implants of the present invention can be for the purpose ofachieving fusion. The upper and lower surfaces of the fusion implantscan include at least one opening, each in communication with the other,to permit for the growth of bone from vertebral body to adjacentvertebral body through the implant. The implant can have an internalchamber and may also have an access opening for accessing the internalchamber, in which case the implant can further have a cover such as acap 101′ (shown in FIG. 1A) to close the access opening at least inpart. Openings in the upper and lower surfaces of the implant cancommunicate with the internal chamber to permit further growth of bonefrom vertebral body to adjacent vertebral body through the implant. Theinternal chamber can contain bone growth promoting materials, includingbut not limited to, bone, bone morphogenetic proteins, hydroxyapatite,and genes coding for the production of bone. The implants of the presentinvention can be formed of a material that intrinsically participates inthe growth of bone from one of the adjacent vertebral bodies to theother of the adjacent vertebral bodies.

While various embodiments of the present invention are presented by wayof example only and not limitation, common to each of them, is that theconfiguration of the surface is based on a plurality of surfaceprojections disposed in arrays, each surface projection comprising atleast one leading facet and at least one opposing trailing facet, inwhich the leading facet has a length greater than the trailing facet andthe trailing facet has a steeper slope than the slope of the leadingfacet. The surface configuration is located on at least a portion of oneof the opposed vertebral body engaging surfaces of the spinal implant.

While the implant shown in FIGS. 1, 2, and 3 is an interbody spinalfusion implant, it is appreciated that the surface configuration of thepresent invention is applicable to any interbody spinal fusion implants,including but not limited to, an artificial disc or motion preservingdevice having opposed surfaces incorporating the present inventiveteachings for engaging each of the adjacent vertebral bodies.

It is believed that the operation and construction of the presentinvention will be apparent from the foregoing description and, while theinvention shown and described herein has been characterized asparticular embodiments, changes and modifications may be made thereinwithout departing from the spirit and scope of the invention as definedin the following claims.

1. An interbody spinal implant for insertion between adjacent vertebralbodies of a human spine, said implant comprising: a leading end forintroduction of said spinal implant into the spine, an opposite trailingend, spaced apart sides therebetween, and a mid-longitudinal axispassing through said leading and trailing ends; opposite upper and lowersurfaces between said leading and trailing ends and said spaced apartsides, said upper surface adapted for placement in engagement with thebone of one of the vertebral bodies and said opposite lower surfaceadapted for placement in engagement with the bone of the other of thevertebral bodies when said implant is placed between the adjacentvertebral bodies; and a plurality of surface projections formed on saidupper and lower surfaces of said implant, at least a first and a secondof said surface projections each having a maximum height, at least oneof said surface projections having a top, a forward facet directed atleast in part toward the leading end, a rearward facet directed at leastin part toward the trailing end, and opposed side facets convergingtoward one another between said forward facet and said rearward facet tointersect each other and form a peak at the top of said at least one ofsaid surface projections, said peak of said at least one of said surfaceprojections overlying at least a portion of another of said surfaceprojections, said forward facet and said rearward facet having a lengthand a slope, the length of said forward facet being longer than thelength of said rearward facet, said forward facet and said rearwardfacet both declining from said maximum height, in a direction towardsaid leading end, said forward facet having converging sides and amaximum width between said converging sides, said maximum width of saidforward facet being greater than said maximum height of said at leastone of said surface projections.
 2. An interbody spinal implant forinsertion between adjacent vertebral bodies of a human spine, saidimplant comprising: a leading end for introduction of said spinalimplant into the spine, an opposite trailing end, spaced apart sidestherebetween, and a mid-longitudinal axis passing through said leadingand trailing ends; opposite upper and lower surfaces between saidleading and trailing ends and said spaced apart sides, said uppersurface adapted for placement in engagement with the bone of one of thevertebral bodies and said opposite lower surface adapted for placementin engagement with the bone of the other of the vertebral bodies whensaid implant is placed between the adjacent vertebral bodies; and aplurality of surface projections formed on said upper and lower surfacesof said implant, said surface projections including adjacent surfaceprojections spaced apart to form a plurality of grooves therebetween, atleast one of said grooves having a horizontal cross-sectional shape thatis one of a v-shape, u-shape, and a box-like shape, at least a first anda second of said surface projections each having a maximum height, atleast one of said surface projections having a forward facet directed atleast in part toward the leading end, a rearward facet directed at leastin part toward the trailing end, and opposed side facets directedgenerally toward said spaced apart sides of said implant, respectively,said side facets converging toward One another between said forwardfacet and said rearward facet in a direction away from one of said upperand lower surfaces of said implant said forward facet and said rearwardfacet having a length and a slope, the length of said forward facetbeing longer than the length of said rearward facet, said forward facetand said rearward facet both declining from said maximum height in adirection toward said leading end, said forward facet having convergingsides and a maximum width between said converging sides, said maximumwidth of said forward facet being greater than said maximum height ofsaid at least one of said surface projections.
 3. An interbody spinalimplant for insertion between adjacent vertebral bodies of a humanspine, said implant comprising: a leading end for introduction of saidspinal implant into the spine, an opposite trailing end spaced apartsides therebetween, and a mid-longitudinal axis passing through saidleading and trailing ends; opposite upper and lower surfaces betweensaid leading and trailing ends and said spaced apart sides, said uppersurface adapted for placement in engagement with the bone of one of thevertebral bodies and said opposite lower surface adapted for placementin engagement with the bone of the other of the vertebral bodies whensaid implant is placed between the adjacent vertebral bodies; and aplurality of surface projections formed on said upper and lower surfacesof said implant, at least a first and a second of said surfaceprojections each having at least one forward facing facet directed atleast in part toward said leading end, at least one rearward facetdirected at least in part toward said trailing end, and opposed sidefacets converging toward one another between said forward facet and saidrearward facet, each of said forward facet and rearward facet having alength and a slope, the length of said forward facet being longer thanthe length of said rearward facet, the slope of said rearward facetbeing steeper than the slope of said forward facet; said first andsecond surface projections each having a base and a portion above saidbase, said portion above the base of said first and second surfaceprojections extending outside of the perimeter of the base of arespective one of said first and second surface projections, saidforward facet having converging sides and a maximum width between saidconverging sides, said base of said first surface projection and saidbase of said second surface projection being spaced apart by a distanceas measured along a line transverse to the mid-longitudinal axis of saidimplant, the distance being less than said maximum width of said forwardfacet.
 4. The spinal implant of claim 1, wherein one of said facets isformed in the shape of a triangle having a vertex with an included anglegreater than 90 degrees.
 5. The spinal implant of claim 1, wherein theslope of said rearward facet is steeper than the slope of said forwardfacet.
 6. The spinal implant of claim 1, wherein said rearward facet isat an angle to at least one of said upper and lower surfaces of saidimplant.
 7. The spinal implant of claim 6, wherein said angle is greaterthan 90 degrees.
 8. The spinal implant of claim 1, wherein said surfaceprojections are oriented relative to one another to form an array. 9.The spinal implant of claim 1, wherein said upper and lower surfaces ofsaid implant are at least in part arcuate.
 10. The spinal implant ofclaim 1, wherein at least one of said leading end, trailing end, andsides are curved.
 11. The spinal implant of claim 1, wherein said sidesare curved.
 12. The spinal implant of claim 1, wherein each of saidleading end, trailing end, and sides are curved.
 13. The spinal implantof claim 12, wherein said leading end, trailing end, and sides form acircle.
 14. The spinal implant of claim 1, wherein said upper and lowersurfaces of said implant are at least in part planar.
 15. The spinalimplant of claim 1, wherein said upper and lower surfaces convergetoward each other along at least a portion of the length of saidimplant.
 16. The spinal implant of claim 1, wherein said implantcomprises a material other than bone.
 17. The spinal implant of claim 1,wherein said implant comprises bone.
 18. The spinal implant of claim 17,wherein said bone includes cortical bone.
 19. The spinal implant ofclaim 1, wherein said implant comprises bone growth promoting material.20. The spinal implant of claim 19, wherein said bone growth promotingmaterial is one of bone morphogenetic protein, hydroxyapatite, and genescoding for the production of bone.
 21. The spinal implant of claim 1,wherein said implant is treated with a bone growth promoting substance.22. The spinal implant of claim 1, wherein said implant is a source ofosteogenesis.
 23. The spinal implant of claim 1, wherein said implant isat least in part bioabsorbable.
 24. The spinal implant of claim 1,wherein said implant comprises metal.
 25. The spinal implant of claim24, wherein said metal includes titanium.
 26. The spinal implant ofclaim 1, wherein said implant comprises at least one of a plasticmaterial, a ceramic material, and a porous material.
 27. The spinalimplant of claim 1, wherein said implant is formed of a material thatintrinsically participates in the growth of bone from one of theadjacent vertebral bodies to the other of the adjacent vertebral bodies.28. The spinal implant of claim 1, wherein said implant is a motionpreserving device adapted to space apart and allow motion between theadjacent vertebral bodies.
 29. The spinal implant of claim 1, whereinsaid spinal implant is a fusion implant.
 30. The spinal implant of claim29, wherein said upper and lower surfaces include at least one openingto permit bone growth from adjacent vertebral body to adjacent vertebralbody through said implant.
 31. The spinal implant of claim 29, whereinsaid implant has an internal chamber and an access opening for accessingsaid internal chamber.
 32. The spinal implant of claim 31, wherein saidimplant has a cap for closing said access opening.
 33. The: spinalimplant of claim 31, wherein said upper and lower surfaces include atleast one opening in communication with said internal chamber to permitbone growth from adjacent vertebral body to adjacent vertebral bodythrough said implant.
 34. The spinal implant of claim 31, wherein saidinternal chamber is capable of containing bone growth promotingmaterial.
 35. The spinal implant of claim 34, further comprising saidbone growth promoting material, said bone growth promoting materialbeing one of bone morphogenetic protein, hydroxyapatite, and genescoding for the production of bone.
 36. The spinal implant of claim 1,further comprising at least one opening capable of retaining fusionpromoting materials.
 37. The spinal implant of claim 1, in combinationwith a fusion promoting substance.
 38. The spinal implant of claim 37,wherein said fusion promoting substance includes at least one of bone,bone morphogenetic protein, hydroxyapatite, and genes coding for theproduction of bone.
 39. The spinal implant of claim 1, wherein each ofsaid surface projections have a base, at least two of said bases beingadjacent to one another.
 40. The spinal implant of claim 1, wherein eachof said surface projections have a base, at least two of said basesbeing spaced apart from one another along a direction generally parallelto the mid-longitudinal axis of said implant.
 41. The spinal implant ofclaim 1, wherein each of said surface projections have a base, at leasttwo of said bases being spaced apart from one another along a directiongenerally transverse to the mid-longitudinal axis of said implant. 42.The spinal implant of claim 1, wherein another of said surfaceprojections has a forward facet, said forward facets of said surfaceprojections facing the same direction.
 43. The spinal implant of claim1, wherein said peaks of at least two of said surface projections arealigned along lines that are at least one of perpendicular, parallel,and diagonal to the mid-longitudinal axis of said implant.
 44. Thespinal implant of claim 1, wherein said peaks of at least two of saidsurface projections are at the same height above one of said upper andlower surfaces of said implant.
 45. The spinal implant of claim 1,wherein adjacent side facets of adjacent surface projections are spacedapart to define a groove therebetween.
 46. The spinal implant of claim1, wherein a plurality of adjacent surface projections are spaced apartto forma plurality of grooves therebetween.
 47. The spinal implant ofclaim 46, wherein at least one of said grooves is parallel to themid-longitudinal axis of said implant.
 48. The spinal implant of claim46, wherein at least two of said grooves cross each other.
 49. Thespinal implant of claim 3, wherein said rearward facet is at an angle toat least one of said upper and lower surfaces of said implant.
 50. Thespinal implant of claim 49, wherein said angle is greater than 90degrees.
 51. The spinal implant of claim 3, wherein said surfaceprojections are oriented relative to one another to form an array. 52.The spinal implant of claim 3, wherein said upper and lower surfaces ofsaid implant are at least in part arcuate.
 53. The spinal implant ofclaim 3, wherein at, least one of said leading end, trailing end, andsides are curved.
 54. The spinal implant of claim 3, wherein said sidesare curved.
 55. The spinal implant of claim 3, wherein each of saidleading end, trailing end, and sides are curved.
 56. The spinal implantof claim 55, wherein said leading end, trailing end, and sides form acircle.
 57. The spinal implant of claim 3, wherein said upper and lowersurfaces of said implant are at least in part planar.
 58. The spinalimplant of claim 3, wherein said upper and lower surfaces convergetoward each other along at least a portion of the length of saidimplant.
 59. The spinal implant of claim 3, wherein said implantcomprises a material other than bone.
 60. The spinal implant of claim 3,wherein said implant comprises bone.
 61. The spinal implant of claim 60,wherein said bone includes cortical bone.
 62. The spinal implant ofclaim 3, wherein said implant comprises bone growth promoting material.63. Thespinal implant of claim 62, wherein said bone growth promotingmaterial is one of bone morphogenetic protein, hydroxyapatite, and genescoding for the production of bone.
 64. The spinal implant of claim 3,wherein said implant is treated with a bone growth promoting substance.65. The spinal implant of claim 3, wherein said implant is a source ofosteogenesis.
 66. The spinal implant of claim 3, wherein said implant isat least in part bioabsorbable.
 67. The spinal implant of claim 3,wherein said implant comprises metal.
 68. The spinal implant of claim67, wherein said metal includes titanium.
 69. The spinal implant ofclaim 3, wherein said implant comprises at least one of a plasticmaterial, a ceramic material, and a porous material.
 70. The spinalimplant of claim 3, wherein said implant is formed of a material thatintrinsically participates in the growth of bone from one of theadjacent vertebral bodies to the other of the adjacent vertebral bodies.71. The spinal implant of claim 3, wherein said implant is a motionpreserving device adapted to space apart and allow motion between theadjacent vertebral bodies.
 72. The spinal implant of claim 3, whereinsaid spinal implant is a fusion implant.
 73. The spinal implant of claim72, wherein said upper and lower surfaces include at least one openingto permit bone growth from adjacent vertebral body to adjacent vertebralbody through said implant.
 74. The spinal implant of claim 72, whereinsaid implant has an internal chamber and an access opening for accessingsaid internal chamber.
 75. The spinal implant of claim 74, wherein saidimplant has a cap for closing said access opening.
 76. The spinalimplant of claim 74, wherein said upper and lower surfaces include atleast one opening in communication with said internal chamber to permitbone growth from adjacent vertebral body to adjacent vertebral bodythrough said implant.
 77. The spinal implant of claim 74, wherein saidinternal chamber is capable of containing .bone growth promotingmaterial.
 78. The spinal implant of claim 77, further comprising saidbone growth promoting material, said bone growth promoting materialbeing one of bone morphogenetic protein, hydroxyapatite, and genescoding for the production of bone.
 79. The spinal implant of claim 3,further comprising at, least one opening capable of retaining fusionpromoting materials.
 80. The spinal implant of claim 3, in combinationwith a fusion promoting substance.
 81. The spinal implant of claim 80,wherein said fusion promoting substance includes at least one of bone,bone morphogenetic protein, hydroxyapatite, and genes coding for theproduction of bone.
 82. The spinal implant of claim 3, wherein said baseof said first surface projection and said base of said second surfaceprojection are adjacent to one another.
 83. The spinal implant of claim3, wherein said base of said first surface projection and said base ofsaid second surface projection are spaced apart from one another along adirection generally parallel to the mid-longitudinal axis of saidimplant.
 84. The spinal implant of claim 3, wherein said base of saidfirst surface projection and said base of said second surface projectionare along a line generally transverse to the mid-longitudinal axis ofsaid implant.
 85. The spinal implant of claim 3, wherein said forwardfacets of each of said first and second surface projections face thesame direction.
 86. The spinal implant of claim 3, wherein said opposedside facets are directed generally toward said spaced apart sides ofsaid implant, respectively, said side facets converging toward eachother in a direction away from one of said upper and lower surfaces ofsaid implant.
 87. The spinal implant of claim 3, wherein said opposedside facets intersect each other.
 88. The spinal implant of claim 87,wherein said opposed side facets converge to form a peak at the top ofsaid surface projection.
 89. The spinal implant of claim 88, whereinsaid peaks of at least two of said surface projections are aligned alonglines that are at least one of perpendicular, parallel, and diagonal tothe mid-longitudinal axis of said implant.
 90. The spinal implant ofclaim 88, wherein said peak of said first surface projection overlies atleast a portion of said second surface projection.
 91. The spinalimplant of claim 88, wherein said peaks of said first and second surfaceprojections are at the same height above one of said upper and lowersurfaces of said implant.
 92. The spinal implant of claim 86, whereinadjacent side facets of adjacent surface projections are spaced apart todefine a groove therebetween.
 93. The spinal implant of claim 86,wherein a plurality of adjacent surface projections are spaced apart toform a plurality of grooves therebetween.
 94. The spinal implant ofclaim 93, wherein at least one of said grooves is parallel to themid-longitudinal axis of said implant.
 95. The spinal implant of claim93, wherein at least two of said grooves cross each other.
 96. Thespinal implant of claim 93, wherein at least one of said grooves has ahorizontal cross-sectional shape that is one of a v-shape, u-shape, anda box-like shape.
 97. The spinal implant of claim 1, wherein saidimplant has a width and a height, the width of said implant beinggreater than the height.
 98. The spinal implant of claim 1, wherein saidforward facet, said rearward facet, and said opposed side facets eachform a triangle.
 99. The spinal implant of claim 1, wherein said upperand lower surfaces each include a plurality of openings to permit bonegrowth from adjacent vertebral body to adjacent vertebral body throughsaid implant.
 100. The spinal implant of claim 3, wherein said implanthas a width and a height, the width of said implant being greater thanthe height.
 101. The spinal implant of claim 3, wherein said forwardfacet, said rearward facet, and said opposed side facets each form atriangle.
 102. The spinal implant of claim 3, wherein said upper andlower surfaces each include a plurality of openings to permit bonegrowth from adjacent vertebral body to adjacent vertebral body throughsaid implant.
 103. The spinal implant of claim 1, wherein saidconverging sides of said rear facet form an apex having an includedangle greater than 90 degrees between said converging sides.
 104. Thespinal implant of claim 1, wherein said forward facet is directed onlytoward the leading end.
 105. The spinal implant of claim 1, wherein saidat least one surface projection has a base, the maximum height beingless than a length of said base.
 106. The spinal implant of claim 3,wherein said converging sides of said rearward facet are arranged toform an apex having an included angle greater than 90 degrees.
 107. Thespinal implant of claim 3, wherein said forward facet is directed onlytoward the leading end.
 108. The spinal implant of claim 3, wherein saidat least one first and second surface projections each have a maximumheight that is less than a length of said base.
 109. The spinal implantof claim 1, wherein said at least one surface projection has a base witha maximum width greater than the maximum height.
 110. The spinal implantof claim 3, wherein said base of said first and second surfaceprojections has a maximum height and a maximum width greater than themaximum height.